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Full text of "Modern Mechanical Engineering Vol-I"

72                                  PATTERN-MAKING

The fitting of the end core prints depends on the relative diameters of
prints and shaft. If the difference is only that due to the thickness of metal
in the shaft, prints are turned on an extension of the lagging (figs. 34 and
36). But if they have to core out a large moulding, then they are better
fitted separately (fig. 35), the lags terminating with the moulding. When
large square bases are fitted to columns, these are prepared separately and
attached. The square prints being large, are boxed up and screwed
against the end of the column and its flange (fig. 37).

Fluted Columns.—The problem in these is that of providing for
delivery of the undercut flutes. The pattern shaft is built with lags, having
flats to receive loose strips in which the flutes are planed. The divisions

Fig. 37.—Method of Fitting a Square Base and its Print

between the strips are determined by the amount and direction of undercut.
In the withdrawal the shaft is taken out first, then the loose pieces adjacent
to the mould joint are removed, and finally those in the bottom. This will
be clear from the section (fig. 38).

In the construction of these patterns, the internal shaft, the body which
forms a backing for the fluted strips, is prepared; the strips are attached to
it with screws put in from within the body, to be taken out in the mould;
and the strips are turned. The edges of the flutes are divided round and
marked along, the strips removed, and the flutes planed. To permit of
planing through, the end pieces where the flutes terminate are screwed
temporarily. Fig. 39 shows a column section where the body is of cast iron
made for permanent service. Metal screws hold the lags, being tapped into
plates sunk in the flute strips.

The cores for columns are usually swept against the edges of boards,
unless large numbers are required, when they are rammed in a half-box,
each half-core being united to its fellow. In plain and moulded columns
the whole of the core can be swept, including the enlarged portions for the
mouldings. But if there is a large square base, as in figs. 37 and 38, or a